There are many sources on the Web for information concerning Charina Bottae -
Rubber Boas. Unfortunately, much of it contains some inaccurate information.
Below are some of my favorite links concerning Rubber Boas.

BurkeMuseum
Excellent information about WA. Note that they are found in actual deserts too
(<10" rain annually) as well as the habitats described. Note that on the eastern
border there are five data points, but very little green. This map is heavily
weighted towards moist habitats, but ignores the arid areas they also populate.
See R.F.Hoyer's comments about probable range in
WA.

State of Utah Includes link to a rang map for Utah (although probably more
widespread than shown). Beware though! This page has misinformation about what
they eat, and wild populations do not give birth every year!